羟乙基瓜尔胶中羟乙基摩尔取代度以及取代位置的表征

本文探索了表征羟乙基瓜尔胶(HEG)中羟乙基摩尔取代度(MS)以及取代位置的化学方法。当反应温度为110℃,时间为14hr,HEG中羟基与混酐比例为1:2.5时,用混酐化学法可准确测定HEG的羟乙基MS,测定结果与计算值的相对误差小于10%。在pH=10.30和0℃的条件下,瓜尔胶的伯羟基被2,2,6,6-四甲基哌啶氮氧化物(TEMPO)-NaClO-NaBr体系选择性氧化成羧基,由此可表征羟乙基链段的取代位置。在瓜尔胶醚化生成羟乙基瓜尔胶的过程中,醚化反应并不是完全发生在伯羟基上。伯羟基的反应活性是仲羟基的6-10倍。随着MS的增大,连接在仲羟基上羟乙基链段占所有羟乙基链段的比例逐渐增大,当MS=0.4时该比例基本不再变化,为40%左右。     

对甲苯磺酸-乙酸酐化学法测定羟乙基瓜尔胶羟乙基摩尔取代度

本文用模型小分子一缩二乙二醇的醚键断裂实验证明了可行性,羟乙基瓜尔胶上的羟乙基链段与过量对甲苯磺酸-乙酸酐在130℃下反应14hr,醚键完全断裂生成酯,并在pH=11条件下煮沸1hr使酯完全水解,转变为乙二醇。通过1H-NMR定量乙二醇,即可准确得到羟乙基瓜尔胶的羟乙基摩尔取代度。     

羟丙基瓜尔胶的制备及表征

瓜尔胶(guar gum)是一种天然半乳甘露聚糖,其水溶性和增稠性很好,广泛用做增稠剂、破乳剂等。原粉胶溶解较慢、水不溶物含量高、粘度不易控制,人们常利用化学手段改变其理化特性以满足实际工业生产需要,羟丙基化是有效的手段之一,但对羟丙基化的表征较为困难。S．     

高碘酸钠氧化法测定羟丙基瓜尔胶上仲羟基取代度

高碘酸钠氧化可以使邻羟基C-C键发生高选择性断裂, 同时产生两分子醛基. 在pH=4.3及25 ℃的条件下, 对瓜尔胶及其衍生物羟丙基瓜尔胶进行高碘酸钠氧化, 采用红外光谱与核磁共振谱对氧化产物结构进行了表征. 结果表明, 氧化后的瓜尔胶和及羟丙基瓜尔胶结构中醛基主要以半缩醛的形式存在. 通过测定高碘酸钠的消耗量得到不同摩尔取代度羟丙基瓜尔胶糖单元上邻羟基的含量, 结合概率分析方法, 确定摩尔取代度分别为0.04, 0.14, 0.36, 0.51, 0.78, 1.05和1.53的羟丙基瓜尔胶在仲羟基上取代度分别为0.02, 0.09, 0.18, 0.30, 0.46, 0.59和1.03, 与其它方法得到的结果一致.     

羟丙基瓜尔胶在离子液体中的制备

本文以离子液体1-烯丙基-3-甲基咪唑氯盐(AmimCl)为反应介质,以氢氧化钠为催化剂合成了羟丙基瓜尔胶(HPG),并通过1H NMR确定了产品的摩尔取代度。探讨了水的用量、环氧丙烷的用量、反应温度和反应时间对摩尔取代度的影响。在水与瓜尔胶的质量比为1.7、氢氧化钠与瓜尔胶的质量比为5%、环氧丙烷与瓜尔胶的质量比为3.5、反应温度为60℃和反应时间为12h的条件下,摩尔取代度(MS)可以达到0.76。同时发现在不加催化剂NaOH的情况下,瓜尔胶在AmimCl中的羟丙基化反应同样可以发生,只是得到的HPG的MS相对较小。     

羧甲基羟丙基瓜尔胶的流变特性

考查了羧甲基羟丙基瓜尔胶溶液的流变特性,发现其水溶液呈典型的假塑性,不同浓度下溶液表观粘度随剪切速率的变化可以用Ostwald-Dewaele方程描述;零切粘度与温度的关系符合Andrade方程;溶液的粘度在酸性条件下随溶液pH的减小迅速降低,在碱性条件下则变化不大;溶液对NaCl很敏感,表现出典型的聚电解质的特征。     

葡萄糖接枝瓜尔胶的合成及表征

本文在研究1,6-脱水葡萄糖均聚的基础上,提出了一种用1,6-脱水葡萄糖对瓜尔胶进行绿色化改性的新方法,并通过核磁对瓜尔胶的葡萄糖接枝产物进行表征,发现随着1,6-脱水葡萄糖与瓜尔胶质量比的增加,产物的葡萄糖摩尔取代度逐渐增大,当1,6-脱水葡萄糖与瓜尔胶质量比为3:1时,共聚产物的摩尔取代度可达0.6.1,6-脱水葡...     

原料配比对羟丙基-β-环糊精取代度的影响

以β-环糊精、氢氧化钠和环氧丙烷为原料,通过改变原料配比合成了不同取代度的羟丙基-β-环糊精(HP--βCD).利用1H NMR对样品进行了表征,进而计算了产物的取代度.结果表明,当固定β-环糊精与氢氧化钠用量摩尔比为1∶6,且环氧丙烷用量低于18倍的β-环糊精用量时,HP--βCD的取代度随环氧丙烷用量的增加呈现规律性增加,有利于获得所需取代度的HP--βCD.     

紫外光谱法测定羟丙基-β-环糊精平均取代度

本实验以丙二醇为基准物作标准曲线,以单、双取代2-羟丙基-β-环糊精作为标准样品,建立了一种利用紫外光谱仪测定羟丙基-β-环糊精平均取代度的新方法。羟丙基-β-环糊精与浓硫酸在100℃水浴中加热反应3min,冷却后加入3%茚三酮溶液,25℃水浴中放置100min显色,用1cm比色皿于588nm处测定吸光值。通过标准曲线查出相应丙二醇的含量,换算出平均取代度。所测定的单、双取代2-羟丙基-β-环糊精平均取代度的相对误差分别为6.67%和2.81%。利用这种方法测定了在不同反应工艺条件下得到的羟丙基-β-环糊精的平均取代度,并与质谱法、核磁共振方法所测定的结果进行了比较。     

元素分析法同时测定羟丙基壳聚糖的取代度和水分

建立了利用CHN元素分析法同时测定羟丙基壳聚糖(HPCS)的取代度和水分含量的新方法。方法可作为羟丙基壳聚糖取代度的标准方法,特别适合于吸水性较强的干燥法难以奏效的羟丙基壳聚糖的水分测定。其计算方法也可用于其他壳聚糖衍生物的测定研究。     

N,N-二乙基胺乙基取代瓜尔胶的合成及结构表征

在碱催化条件下,利用N,N-二乙基氯乙胺盐酸盐与瓜尔胶和羟丙基瓜尔胶一步法合成得到N,N-二乙基胺乙基瓜尔胶和N,N-二乙基胺乙基羟丙基瓜尔胶。结果显示合成过程中温度、反应时间、羟丙基取代度及溶剂等因素对产品分子量和N,N-二乙基胺乙基取代度有影响。通过红外光谱和核磁法对N,N-二乙基胺乙基瓜尔胶和羟丙基N,N-二乙基胺乙基瓜尔胶的分子结构进行了分析,并通过碳谱对N,N-二乙基胺乙基在瓜尔胶分子链中糖环上的取代分布进行了分析。     

Syntheses and properties of superabsorbent composites based on natural guar gum and attapulgite

Utilization of raw materials available in nature and their application to derive other useful products without any adverse impact on the environment has long been a desired goal. In this work, guar gum (GG) and attapulgite (APT) clay were used as raw materials for preparing guar gum‐g‐poly(acrylic acid)/attapulgite (GG‐g‐PAA/APT) superabsorbent composites through the graft copolymerization of GG, partially neutralized acrylic acid (AA) and APT in aqueous solution. The effects of reaction conditions such as concentrations of the initiator and crosslinker, APT content, etc. on water absorbency were investigated. The composite prepared under optimal conditions gave the best absorption of 529 g/g sample in distilled water and 61 g/g sample in 0.9 wt% NaCl solution. Swelling behaviors revealed that the superabsorbent composites retained a high water absorbency over a wide pH range of 4–11, and the developed composites also exhibited improved reswelling and water‐retention capabilities. The superabsorbent composites can be utilized as eco‐friendly water‐manageable materials for agricultural and horticultural applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Fast and excellent healing of hydroxypropyl guar gum/poly(N,N‐dimethyl acrylamide) hydrogels

In this article, a fast and high efficient healing hydroxypropyl guar gum (HPG)/poly(N,N‐dimethyl acrylamide) (PDMA) hydrogel is prepared by a facile synthesis method. HPG networks are formed through hydrogen‐bond interaction between the hydroxyl groups in the HPG chains, and PDMA networks are self‐crosslinked without any chemical crosslinker. The cut hydrogel could heal when nanosilica solution is chosen as the connector that is related to the adsorption of polymer to the surface of nanosilica. The fracture stress of the HPG/PDMA gels presents a fast and almost full recovery within a short time (1 min), while the recovery of fracture strain and elastic modulus is related to time in 2 h. The healing efficiency of HPG/PDMA gel is investigated as a function of healing time, HPG content, and N,N‐dimethyl acrylamide content. The microscopic healing process and healing mechanism are also discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 239–247     

Thermal and mechanical properties of cationic guar gum/poly(acrylic acid) hydrogel membranes

Novel hydrogel membranes (coded as GA) based on cationic guar gum (CGG) and poly(acrylic acid) (PAA) were synthesized with various feed compositions. Their structure and properties were studied by Fourier transform infrared spectra, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analyses and tensile tests. The structure analyses indicated that there existed strong electrostatic interaction between CGG and PAA, which resulted in uniform structure and complete miscibility between the two components. On the basis of thermogravimetric analyses, the activation energies (E_a) of the first degradation of the membranes increased from 34.5 to 77.1 kJ/mol with an increase of CGG content, while the residual ratios of the membranes increased from 7.6 to 36.1 wt% at 600 °C. This indicated an elevated thermal stability of PAA-based materials through an introduction of CGG. The tensile tests exhibited the mechanical properties of the membranes were improved with an increase of CGG content, and the maximum value of 41.1 MPa was reached.